The findings of this study were as follows: (i) approximately 30% of gastric cancer patients were APCA-positive; (ii) high proportions of MUC6, MUC5AC, and PD-L1 expression, greater infiltration of CD3/Foxp3/PD1-positive cells, and greater B. cereus abundance were associated with pure AIG; (iii) APCA-related gastric cancer tended to have a better prognosis. Here, MUC5AC is linked to gastric cancer.